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The engine:
Much to everyoneís surprise, opening up the ATV engine isnít all that different from a look inside the bike engine. The only major change is a shorter stroke of the crank bringing displacement down to the 439cc mark. Vet riders might remember that two seasons back (during the YFZ450ís development) the legal pro class displacement limit was 440cc. Other than beefing up a few components here and there for long levity, a small timing change and a push button start, ATV buyers got the same engine riders like Tim Ferry and Chad Reed were using to win races in the dirt bike world.

Yamaha was not pleased when we returned their YFZ butchered from a plasma cutter. Actually, Yamaha displayed this YFZ cutaway at the ATV Expo in Louisville.

These minor changes added up to a power band that was smoother and more controllable for use in an ATV setup. Yamaha didnít tame the engine to slow it down, they actually made it better. Although power comes on strong in the midrange it is still relatively smooth compared to itsí two wheeled cousin. By keeping the Keihin FCR carburetor the YFZ is awarded with the best throttle response ever from an ATV engine. To keep the high revving engine cool a dry sump oil system sits directly in front of the engine holding enough surplus oil to keep the twin cam engine spinning exactly the way it needs to be.

Fully adjustable and rebuildable front shocks set the YFZ apart from all previous sport ATVs.

The chassis:
Perhaps we should offer the highest props here. Up until the introduction of the YFZ there had only been one way to build a successful ATV racing chassis, modify a Honda design. Yamaha went through the paces designing a chassis that met the current standards in every way yet shared no resemblance to anyone elseís platform. Yamaha has constantly improved on their chassis building techniques and arrived at a first class design with the YFZ.

The superb rear suspension design allows a seat bounce in tight sections.

Although the main construction remains a mild steel round tube design the limits have been slightly pushed by adding an aluminum sub-frame. Several other chassis components have been cast from aluminum such as the hubs and swing-arm, which significantly reduce the accepted weight of a production 4 stroke ATV.

The handling is spot-on; in fact it is the most spot on weíve ever seen from Yamaha. The turning radius is a little wide considering just how controllable the machine is. Steering is very predictable and reminds us of an old friend, not the new high tech ATV that it is.

Suspension is top notch for current production ATVs. Each shock is fully adjustable and rebuildable. Settings are dialed in well for the general public but racers may want to add a small amount of sag and a couple clicks of compression to the rear. Any major suspension company can also perform a complete race rebuild on the complete set of shocks for about the price of a front or rear after market shock.